With continuous development of display technologies, people desire more and more for more realistic images. Recently, there have been three-dimensional (3D) display (also referred to as stereoscopic display) realized by using various techniques, which brings viewers more realistic stereoscopic effect compared to 2D display, and therefore is favorable and preferred.
The reason why the objects are three-dimensional from the view of people is that people have two eyes with a certain distance therebetween, and a 3D image is merged by the brain from two slightly different images of objects generated on the retina of two eyes. Stereoscopic display technology utilizes the rationale of stereoscopic imaging for human eyes, i.e., there are two slightly different images of objects viewed from different viewing angles by human eyes, and the two slightly different images are then merged by the brain to a stereoscopic vision. Currently, a common stereoscopic display method is the method adopting polarizers, which utilizes different polarization angles of light, to allow the lights in different polarization states to pass through the two polarizers respectively, and to project the two images with slight differences into left and right eyes, respectively, so as to bring three-dimensional stereoscopic perception to human. However, such stereoscopic display method is required for viewers to wear matching stereoscopic polarizing glasses to view 3D image, which often results in discomfort to viewers, especially to viewers already wearing a pair of glasses which are more difficult. Therefore, there are methods to view stereoscopic images without wearing stereoscopic glasses, i.e., methods for stereoscopic display with naked eyes, to satisfy the requirements of viewers.
FIGS. 1a and 1b disclose a partially sectional view of a conventional 2D/3D switchable display apparatus. As shown in FIGS. 1a and 1b, the 2D/3D switchable display apparatus includes a liquid crystal display panel 2 and a liquid crystal lens 3 provided at one side of the liquid crystal display panel 2 adjacent to the viewer. The liquid crystal display panel 2 has first pixels 21 (pixels filled by black in FIGS. 1a and 1b) and second pixels 22 (pixels unfilled in FIGS. 1a and 1b). The liquid crystal lens 3 includes a first substrate 31 adjacent to the viewer, a second substrate 32 far from the viewer, and a medium layer 33 interposed between the first substrate 31 and the second substrate 32. A first transparent electrode 311 is provided on one side of the first substrate 31 adjacent to the second substrate 32, and a second transparent electrode 321 is provided on one side of the second substrate 32 adjacent to the first substrate 31, the first transparent electrode 311 and the second transparent electrode 321 generally both being formed by indium tin oxide (ITO). There are a plurality of elongated arch-shaped spaces 34 at one side of the medium layer 33 adjacent to the second substrate 32, and liquid crystal 36 having anisotropic optical properties is filled in the arch-shaped space 34, and the refractive index n1 of the medium layer 33 and the refractive index ne of major axis of the liquid crystal 36 as well as the refractive index no of minor axis satisfy the following:n1=no<ne.
The arch-shaped space 34 has a curved surface adjacent to the first substrate 31 and a flat surface adjacent to the second substrate 32, and the curved and flat surfaces on the arch-shaped space 34 are both provided with an alignment layer 35, and, the alignment direction of the alignment layers 35 is the same as the direction of transmission axis of a corresponding light emitting polarizer in the liquid crystal display panel 2, as shown in FIG. 1a, the alignment directions of the alignment layers 35 on respective surface inside the arch-shaped space 34 are perpendicular to the paper surface. The 2D/3D switchable display apparatus can realize the switching between 2D display and 3D display by altering the voltage between the first transparent electrode 311 and the second transparent electrode 321 located in the liquid crystal lens 3.
As shown in FIG. 1a, when there is no voltage applied between the first transparent electrode 311 and the second transparent electrode 321, the major axis of liquid crystal 36 inside the arch-shaped space 34 is aligned along the direction parallel to the alignment direction, i.e., aligned perpendicularly to the paper surface as shown in FIG. 1a, at this time, the refractive index of liquid crystal 36 is ne, and because ne<n1, the liquid crystal lens 3 is in a refracting mode, and converges the light incident from the second substrate 32, and in this case, the light emitted from the first pixels 21 and the second pixels 22 in the liquid crystal display panel 2 selectively enters the right and left eyes of the viewer, respectively, along the different propagation paths. Images entering the right and left eyes of the viewer are also two images with optical parallax since the images that the first pixels 21 and the second pixels 22 display are two images with optical parallax, and are merged by the brain to form a stereoscopic vision, therefore presenting a 3D display mode.
As shown in FIG. 1b, when there is a certain voltage applied between the first transparent electrode 311 and the second transparent electrode 321, an electric field is formed between the first transparent electrode 311 and the second transparent electrode 321, the major axis of liquid crystal 36 inside the arch-shaped space 34 is aligned along the direction of the electric field, i.e., aligned perpendicularly to the first substrate 31 and second substrate 32 as shown in FIG. 1b, at this time, the refractive index of liquid crystal 36 is no, and because noo=n1, the liquid crystal lens 3 is in a non-refracting mode, and the light incident from the second substrate 32 will not be refracted through liquid crystal 36 and the medium layer 33, but remains its original direction of propagation, and in this case, the light emitted from the first pixels 21 and the second pixels 22 in the liquid crystal display panel 2 simultaneously enters the right and left eyes of the viewer after passing through the liquid crystal lens 3, and the same image displayed on the liquid crystal display panel 2 will be received by the right and left eyes, therefore presenting a 2D display mode.
However, The above liquid crystal lens 3 based display apparatus for the switching of 2D display and 3D display is based on the polarized light, and as a result, such display apparatus now is only suitable for liquid crystal display employing the polarizer, but not for display device using non-polarized light mode such as cathode ray tube display (CRT), plasma display panel (PDP) or organic light emitting diode display (OLED), etc. Moreover, because the liquid crystal 36 is anisotropic, which has a refractive index ne of the major axis varied depending on the direction of incident light, and the medium layer 33 is isotropic material, the liquid crystal lens 3 is largely direction-dependent. In addition, as the liquid crystal 36 is affected by anchoring force as a result of requirement for alignment layer 35, the liquid crystal lens 3 requires a larger driving voltage, resulting in higher power consumption of the liquid crystal lens 3.